Proprioception is not one of the 5 senses but it is probably the most central sense for partner dancing.
It’s textbook definition is: The awareness of your own body in space.
In partner dance we use it to handle expanded responsibilities. Keeping track of our own body, and our partner’s body.
This amalgamates your own bodies direct proprioceptive sensory data as well as touch to create a mental awareness of your partner’s body like your own. This is a similar use of proprioception to tool use. This would seem quite complicated with a partner who’s body is far more complex in joints and mechanics to a day to day tool. However understanding a body is what the proprioceptive analyses in the brain was designed for and sympathetic use to understand another body is something it does instinctively.
With good proprioceptive awareness you can do crazy things like know where your partner’s foot is, move as a unit with a partner and instinctively follow Mechanics changes in a partner.